A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs). Enhancements to LTE systems are considered so that they can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard.
One of the key enhancements is to support bandwidth up to 100 MHz and be backwards compatible with the existing wireless network system. Carrier aggregation (CA) is introduced to improve the system throughput. With carrier aggregation, the LTE-Advance system can support peak target data rates in excess of 1 Gbps in the downlink (DL) and 500 Mbps in the uplink (UL). Such technology is attractive because it allows operators to aggregate several smaller contiguous or non-continuous component carriers (CC) to provide a larger system bandwidth, and provides backward compatibility by allowing legacy users to access the system by using one of the CCs.
With CA, two or more CCs are aggregated to support wider transmission bandwidth up to 100 MHz. A UE with reception and/or transmission capabilities for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells. When CA is configured, the UE has only one RRC connection with the network. At RRC connection establishment/reestablishment or handover, one serving cell provides the NAS mobility information. At RRC connection reestablishment or handover, one serving cell provides the security input. This cell is referred to as the primary serving cell (PCELL), and other cells are referred to as the secondary serving cells (SCELLs). Depending on UE capabilities, SCELLs can be configured to form together with the PCELL as a set of serving cells under CA.
In LTE systems, an eNB may dynamically allocate resources among UEs. Carrier aggregation allows the mobile network to use the bandwidth more efficiently. However, it also increases the complexity of resource management. A light-weighted component-carrier management scheme is thus desirable. One of the issues is how to efficiently activate or deactivate one or more component carriers on a UE. For carrier aggregation, an SCELL is first configured by the network before usage in order to provide necessary information to the UE. A configured SCELL starts in a deactivated state for energy saving. A deactivated SCELL is then activated by the network before the UE can perform defined normal operation.
SCELL activation time should be reasonably small for energy saving. For long activation time, the benefit of fast SCELL activation/deactivation based on dynamic data traffic is lost. The time required for SCELL activation depends on the readiness of SCELL. If the configured SCELL has been measured by UE or UE has valid prior knowledge on synchronization and AGC of the SCELL, activation time can be smaller. On the other hand, if UE does not have any valid prior knowledge on the configured SCELL, activation time will be significantly longer.
A worst-case scenario is that SCELL activation command is received in the earliest possible timing after the SCELL is blindly configured to a UE. In such scenario, there is no valid prior knowledge of the configured SCELL. Such SCELL activation command before valid information of configured SCELL is referred to as blind SCELL activation. Another scenario that requires long SCELL activation time is that part of the prior knowledge is no longer valid so that long SCELL activation procedure is needed to reacquire the knowledge. This happens when deactivated SCELL measurement has been performing regularly. But due to, e.g., high mobility of UE and long measurement cycle, some of the knowledge of the SCELL (e.g., time/frequency synchronization information) cannot be regained through fast tracking techniques based on the prior knowledge. In such case, longer time is required to regain the knowledge. In the example of timing synchronization, longer time are required to use CRS for tracking. In worst scenario, PSS/SSS signals are required for timing acquisition. Mechanisms are required to keep the SCELL activation time small for energy saving and for scheduling gain.